Steph - When I get updates in my email, at the bottom you are given an option 'Unsubscribe From The Thread', yet directly underneath that is one that says 'Unsubscribe From All Threads'. You must have clicked that one by accident.
IF you go to the top of the TMF main page, just under the main heading you see a list of options. Go to USER CP on the top left. Then under Control Panel click Edit Options. Then on your right scroll down to Messaging & Notification, and you should be able to reset it.